Preheat oven to 180 degrees C. Line or grease a muffin tray.
Mix flour, sugar, cocoa, bicarbonate soda and baking powder together in a large bowl.
In another bowl mix the egg, oil, yoghurt and vanilla.
Make a well in the dry ingredients then pour in the wet mixture and combine thoroughly.
Half fill the muffin cases with batter. Make a slight depression in the middle of the cup and place in your piece of chocolate. Careful as too much pressure pushes the chocolate through to the base and ruins the muffin. Top with approximately 1/2 teaspoon of jam per muffin. Top with remaining muffin batter.
Bake for 20 minutes testing the muffins around the edge to ensure that they are cooked.
Leave to sit for 5 minutes before gently removing from the tray and placing on a cake rack.
They can be dusted with a little icing sugar before serving.